Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $199.59   13.732%   $226.9977   $227.00   $227.00   $227.00  
  Purchase #2 $68.30   5.825%   $72.2785   $72.28   $72.30   $72.30  
  Purchase #3 $58.94   11.836%   $65.9161   $65.92   $65.90   $65.90  
  Purchase #4 $68.64   5.743%   $72.582   $72.58   $72.60   $72.60  
  Purchase #5 $212.42   10.328%   $234.3587   $234.36   $234.35   $234.40  
  Purchase #6 $228.47   3.740%   $237.0148   $237.01   $237.00   $237.00  
  Purchase #7 $126.40   8.545%   $137.2009   $137.20   $137.20   $137.20  
  7 purchase totals = $962.76       $1,046.3487   $1,046.35   $1,046.35   $1,046.40